Well now I've gone and done it...

[marrt]

What you have is extra HP above what is required to power all pumps at maximum.

J.J., I'm not sure this is true. In other words, I'm not sure 25 HP will power all pumps to full pressure and speed WHEN the wheel motors and attachment motors are at full design load. For example, there's a hill on my property that has a moderate slope. If I attach the mower, but leave it off, the tractor will climb the hill fine. However, if I turn on the mower and the grass is fairly tall, I can't make it up the hill due to the engine not having enough power. I believe MR has described this behavior in the past too. Since the tractor and mower are driven by different pumps, this suggests we don't have enough HP.

In addition, I can stall the engine by placing the tractor against an immovable object and slowing flooring the tram. This suggests a) my reliefs are set too high in the VV pump or b) the engine doesn't have enough power to break the reliefs before it stalls.

And finally, I've notice others claiming a large increase in "power" from installing a larger engine. In theory, it shouldn't make any difference in power if the engine was originally sized to take advantage of the maximum capacity of the pump and other components.

 

[ponytug]

I would agree; I think that the machines do not have enough power to run all loads at maximum slope, or we would be able to charge hills at full throttle. Therefore, more HP will make a difference to the mower load/slope/speed tradeoff. One way or another, it is all load, aka power, i.e. HP.

I think that this is a fantastic project. Hats off to Gravy for doing it and sharing it with us.

All the best,

Peter

J.J., I'm not sure this is true. In other words, I'm not sure 25 HP will power all pumps to full pressure and speed WHEN the wheel motors and attachment motors are at full design load. For example, there's a hill on my property that has a moderate slope. If I attach the mower, but leave it off, the tractor will climb the hill fine. However, if I turn on the mower and the grass is fairly tall, I can't make it up the hill due to the engine not having enough power. I believe MR has described this behavior in the past too. Since the tractor and mower are driven by different pumps, this suggests we don't have enough HP.

In addition, I can stall the engine by placing the tractor against an immovable object and slowing flooring the tram. This suggests a) my reliefs are set too high in the VV pump or b) the engine doesn't have enough power to break the reliefs before it stalls.

And finally, I've notice others claiming a large increase in "power" from installing a larger engine. In theory, it shouldn't make any difference in power if the engine was originally sized to take advantage of the maximum capacity of the pump and other components.

 

[J_J]

The machines that are designed for slopes should have enough power to do the job at the advertised angle.

As your machine get work/older, it will not meet the specs.

I think some of you are asking the machine to do more than it is designed.

This is just my opinion, but why would you not designed for less HP for the pumps requirement, plus some extra.

Have you ever heard of 110 percent.

Maybe PT is not telling the full story. Like will my 425 climb a 30 degree hill with mower running full out and not stall?

 

[KMA]

FWIW, when I called Terry a while back to ask if my PT422's pumps would handle the EH72 FI (25-28hp) vs the original EH65 (22HP), he said "yeah, no problem".

 

[J_J]

You can turn a hyd pump with any size engine that is above the HP requirement of the pump.

10 GPM at 3000 psi, requires about 21 HP. If that pump /HP was designed for flat ground, then you can expect it to not perform climbing a 30 degree hill.

 

[KMA]

I noticed a marginal improvement in climbing hills with the finish mower engaged. It wasn't night and day, but a bit better. That being said, the bigger engine won't turn it into something it's not.

 

[MossRoad]

Yeah, my 425 will not climb steep hills with the mower engaged. If I shut it off, up we go. So, not enough power to turn the wheel motors and the mower deck motor at the same time in that situation. Is that bad? I don't think so. If I put larger displacement wheel motors, I think I could climb that hill and power the mower at the same time, but I'd sacrifice top speed, which I do use often to get from one side of the place to the other. Although, thinking about it, I wouldn't mind giving up 2mph top speed. On flat land, the PT scoots just fine at full speed. But out in the woods, or hauling a trailer of mulch, etc... I never go top speed. If I ever lose a wheel motor, I may consider a swap, but until then, I'm keeping the thousand bucks in my pocket. :laughing:

 

[MossRoad]

And to be clear, I really have no need to mow that hill. I only brush hog a trail on it a couple times a year. I can do that in the down direction. Its not like I'm mowing vast expanses of lawn on a hillside.

 

[KentT]

I understand JJ's point, IF we were dealing with fixed displacement pumps, matched closely to the output power of the engine...

But, since the tram pump is variable displacement a larger HP engine provides the potential to produce more torque (pressure) at the wheel motors BECAUSE the factory-supplied engines cannot provide both maximum flow and maximum pressure at the same time. Flow (speed) and torque/power (pressure) is ALWAYS a balancing act. We have all experienced the need to "back off on the treadle" to climb a slope, for example, especially when running a PTO implement such as a mower. With a larger HP engine, you would not have to back off the treadle as much... Similarly, when pushing into a pile of dirt with a bucket, the engine would not start to drop RPMs (and eventually stall) as soon...

You would feel the power difference -- though how significant is TBD...

 

[MossRoad]

Makes you wonder if you had more HP available, and you did not back off the pedal as you would with the lower HP engine, would the pump be able to handle the added HP or blow up? Or bypass, I mean. Since none of us have apparently ever hit the bypass on the tram pump, lets add some more HP and push them till they bypass, then back off the HP. Right? :laughing: